Atypical cerebral laterality in adults with persistent developmental stuttering

Background: Two of the most consistent anatomic asymmetries found in the human brain are a larger right than left prefrontal and left than right occipital lobe. Reduced or reversed asymmetries of these regions are considered markers of atypical cerebral laterality, and atypical cerebral laterality has been proposed to increase neural risk for developmental stuttering. Objectives: To learn if atypical prefrontal and occipital lobe asymmetries are more common in adults who stutter vs fluent control subjects and to determine whether lobar size or asymmetry patterns are associated with stuttering severity or language abilities. Methods: Adults with persistent developmental stuttering (n = 16) and matched control subjects (n = 16) had language and stuttering assessments. Subjects were also studied with volumetric MRI scans. Total hemisphere, prefrontal, and occipital lobe regions were measured, and volumes were calculated proportionally to hemisphere volume. Results: Hemisphere and total brain volumes did not differ between the groups. Control subjects had the expected larger right than left prefrontal and larger left than right occipital lobe volume. In contrast, the adults who stutter did not have these asymmetries. Stuttering severity was not associated with specific anatomic configurations, whereas language-processing deficits in adults who stutter were associated with prefrontal and occipital volume reduction. Conclusions: Developmental stuttering is associated with atypical prefrontal and occipital lobe asymmetries. In addition, deficits in language processing were associated with some anatomic measures in the adults who stutter.